This invention relates generally to X-ray generating apparatus, and more particularly to an X-ray tube having a target anode structure which produces a spectrum having line emission at different wavelengths.
The ability to produce specific atomic emission line spectra would provide a unique capability in X-ray analysis. Current technology uses a broad high energy spectrum of X-rays to perform analyses of materials by absorption. The degree of absorption is dependent on the total mass thickness in the X-ray beam, and specificity to the constituent absorbers is lost. However, with the appropriately chosen atomic emission lines in the source spectrum, it would be possible to detect small quantities of a particular element or elements in the presence of large quantities of other absorbers. In general the technique can be applied to any situation in which the concentration and/or spatial distribution of specific elements is required in the presence of other materials. One application of a multi-color X-ray line source would be two-phase flow diagnostics, such as analysis for solid particles including a particular element in a gas stream.
The prior art includes some United States patents showing monochromatic and multi-color X-ray sources, which describe various uses for medical diagnosis, industrial diagnosis of structures, and others. Friedman U.S. Pat. No. 2,998,524 discloses a monochromatic X-ray source including a copper base and a layer of aluminum, which produces only the line radiation, free of the continuum of energy values commonly called Bremsstrahlung or white radiation. Braun et al U.S. Pat. No. 3,943,164 discloses an X-ray tube with an anode target shaped like a disc open toward an electron emitting cathode. Rod-like members are disposed in an annular groove around the anode and provide substantially monochromatic X-radiation when bombarded with electrons. The rod-like target members in different arcuate portions are made of different materials and therefore emit radiation of different wavelengths in sequence as the anode rotates, thus providing a multi-color X-ray line source. Albert U.S. Pat. No. 4,007,375 discloses a multi-color X-ray source in a cathode-ray-type tube shown with four targets on the face of the tube, so that beam deflection can be used to select any one of the targets. Waugh et al U.S. Pat. No. 4,227,112 is of interest for its disclosure of a rotatable X-ray target having an annular focal track with a controlled gradient of target material.